An extruder for producing a polymer melt typically has an intake barrel for taking in, melting, and kneading plastic granules, bottle flakes, or fibers, a degassing drum attached to the intake barrel and drum having a multiple-screw extruder assembly, and an output barrel for discharging the polymer melt. The extruder further has a driven shaft that at least at the degassing drum has for its multiple planet screws a guide body rotationally fixed by a support to the shaft and provided between an upstream cone and a downstream cone. The planet screws have drive gears that at their ends mesh with at least one ring gear fixed in the degassing drum. Thus as the driven shaft rotates about its axis, the planet screws are rotated, thoroughly kneading and mixing the melt passing axially through the extruder and allowing gaseous inclusions to escape at the degassing drum.
In an extruder is disclosed in U.S. Pat. No. 7,513,677 the ratio between the rotation speed and the exact implementation of the geared connection between the planet-screw gears and the ring gear must be coordinated with each other as a function of the polymer to be processed and the required processing task. The use of a more throughput-efficient bevel gearing or spur gearing can be advantageous, depending on the processing task. The ratio for rotation speeds determines degassing efficiencies. Adjust-ment of the rotation speeds requires different bore diameters for the guide body at least at the gearing.
If extruder as set forth in U.S. Pat. No. 7,513,677 is to process different materials, the multiple-screw extruder assembly must be completely removed from the degassing drum and replaced with planet screws of a different pitch and/or with gears of different gear ratios. Typically, however, it is not the extruder screws, but preferably the drive gears and the ring gears that have to be replaced by components of different gear ratios.
The prior art in principle thus requires the entire guide body with its planet screws to be replaced, despite the fact that what is generally required is only a modification of the gears.